This species forms erect thalli, 3-16 cm tall, that are yellowish to brownish or dark red in colour (Featured Image above). Individuals can appear (sub)dichotomous in overall branching with short adventitious branches formed (Image A), to more irregular owing to substantial investments of more developed adventitious branches (Image B). Individuals are attached by a dense investment of descending rhizoids at the base (Image C), these multicellular and branched (Image D). Main axes near the base can be prostrate (attach by rhizoids) and produce laterals that develop into erect axes. The tips are forcipate and strongly inrolled (less so on tetrasporophytes) forming a distinctive feature for many species in this genus (Image E). Apical cells are rounded, while slightly acute cells are produced at the tips on the adaxial surface of some branches (Image E). Primary branches occur every 7-15 segments, and adventitious branches can be infrequent to abundant (Image F). Near the tips this species can be fully corticated (Image G), or with very narrow ecorticate internodal regions (Image H) or have incompletely corticated internodal regions mid to upper thallus (Image I), which are a mix of regular and elongate cortical cells (Image J). Near the tips the segments range from 0.8-0.9 diameters long, approaching ~1.2-1.6 diameters long mid to lower thallus, where axes are fully corticated. Axes can be constricted at the nodes to give a slightly beaded appearance to larger individuals when viewed with the unaided eye. Gland cells are absent, but hyaline cells were observed (Image K), which appear to be hair mother cells as they were observe on individuals that produce numerous hair cells (Image L). Cross section at the nodes reveals 6(7) periaxial cells (Image M). Carposporophytes are barely visible to the unaided eye, 245-290 µm in dimensions (based on few observations), and consist of 1 dominant gonimolobe and 1-2 suppressed gonimolobes (sequential development) and 3-5 associated involucral branchlets (Image N). Tetrasporangial production is concentrated in tiers at the nodes (Image O) with the sporangia largely covered by cortication and irregularly tetrahedral to cruciate (Image P) or decussate (Image Q) in division pattern, 50-71 µm wide by 74-88 µm tall.
This species is common and widespread in the NW Atlantic with collections from RI to central Labrador. It is found growing from mid intertidal pools to subtidal (30 m) on various hard substrata and other algae. This morphospecies corresponds to three genetic groups in the Canadian flora and further taxonomic work is necessary. South of Cape Cod this species could be confused with Ceramium secundatum Lyngbye, but in that species there are 7-9 periaxial cells in cross section, the segments reach 2 diameters in length mid to lower thallus, and the gonimolobes are large (300-600 µm). Confusion with Ceramium sp. 2virgatum is also possible, but that species has 0-1(2) involucral branches associated with its carposporophytes and only a single tier of tetrasporangia with 1-2(3) evident at a time.
Image A. Specimen displaying a largely dichotomous branching habit, as well as regular short adventitious branches (subtidal (3.5 m) on rock, Carrying Cove, New River Beach, NB; GWS030250).
Image B. Irregularly branched subtidal (4 m) specimen growing on Chondrus crispus Stackhouse at Gaulman Pt., NS (GWS032149).
Image C. Dense investment of rhizoids near the base of an erect axis (subtidal (6 m) on Cystoclonium purpureum (Hudson) Batters, Peggys Cove, NS; GWS011705; rehydrated from press).
Image D. Closeup of the multicellular and branched rhizoids (GWS011705; rehydrated from press).
Image E. Inrolled tip with a domed apical cell and slightly acute cells (arrows) on the adaxial surface (GWS030250; rehydrated from press).
Image F. Short adventitious branches (arrows) (GWS030250; rehydrated from press).
Image G. Essentially fully corticated axis (GWS030250; rehydrated from press).
Image H. Corticated axis with slightly ecorticate internodes (arrows) (subtidal (2 m) on rock, Turnagain I., outside village Black Harbour, Labrador, NL; GWS039372; rehydrated from press).
Image I. Axes with incomplete cortication of the internodes (mid intertidal on rock, Eastport, NL; GWS007423; rehydrated from press).
Image J. Incomplete cortication with a mix of typical cells (at the nodes) and elongate (arrows) cortical cell filaments (typically masked when cortication is complete), which can transverse the internodes (GWS007423; rehydrated from press).
Image K. Hyaline gland-like cells (arrows), which appear to be hair mother cells (GWS011705; rehydrated from press).
Image L. Hair cell extending past the cortex (GWS011705; rehydrated from press).
Image M. Cross section reveals the central axial cell surrounded by 6(7) periaxial cells (subtidal (6 m) on rock Peggys Cove, NS; ; GWS011682; rehydrated from press; aniline blue stained).
Image N. Mature and suppressed gonimolobes with three (one in plane of focus; arrow) involucral branches (mid intertidal on Palmaria palmata (Linnaeus) F.Weber & D.Mohr, SE of Beaver Harbour in SCUBA Bay, Bay of Fundy, NB; GWS009893; rehydrated from press).
Image O. Tetrasporangia produced (loosely two rows) at the nodes (mid intertidal pool on algae, semi-exposed, Wallace Cove Lighthouse, NB; GWS031539; rehydrated from press).
Image P. Cruciate division of a tetrasporangium (upper) (GWS007423; rehydrated from press).
Image Q. Decussate division of a tetrasporangium (mid intertidal on Mastocarpus stellatus (Stackhouse) Guiry in pool, SE of Beaver Harbour in SCUBA Bay, NB; GWS009894; rehydrated from press).